Wind profilers can detect wind speed and direction (i.e. velocity) at various altitudes using radars and are typically used for meteorological forecasting and flight planning. Radar based wind profilers can measure wind velocity by observing scattering effects on radio waves due to micro-hydrometers including fog, clouds, and/or mist—so called dull weather phenomena and suspended particles including (but not limited to) thick dust and insets.
Further, radar based systems can detect wind speed and direction by observing the so called Bragg Scattering phenomena caused by natural atmospheric turbulence in the atmosphere. Wind profiling radars typically operate at frequencies near 50 MHz, 400 MHz and 900 MHz because Bragg Scattering conditions are dominate at these relatively lower frequencies. However, Bragg Scattering effects are relatively faint even at these lower frequencies and radars have traditionally relied on larger integration times, larger range cells, and larger antenna arrays to make measurements.
Clear air scatterers (CAS) are small turbulent motions of air associated with ever-present hydrodynamic-thermodynamic instabilities in the atmosphere during clear weather conditions. Such small turbulent motions can track the mean velocity of a volume of wind and exist long enough to reliable detected. Further CAS have a defined nature and are prevalent in the convective boundary layer (CBL) where wind speed and direction measurements are particular useful for meteorological forecasting and/or flight planning. However, CAS in the CBL have very small returns (reflected energy), often two orders of magnitude smaller than returns for fog or clouds and conventional thinking has been that radar's operating in the centimeter to millimeter range in clear weather conditions could not obtain a useable return due to the varying and often small concentrations of CAS.